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01-07-2020, 07:14 PM   #1
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Adapter to fit 39mm Leica threaded lenses to Pentax K50

I own a vintage Reid III camera with a Taylor-Hobson f/2, 2 inch lens. The camera is a British copy of the Leica IIIc and is very highly rated. It sells for about $3000 on eBay. I also own a Leica IIIc with a Nikkor W35C lens which is also highly rated. I always wanted to use these lenses on my K50 to see how good they were, so I ordered an adapter made in China to couple these lenses to my Pentax. The adapter arrived after about 2 weeks and it was very finely manufactured for a cost of about $8 including postage. However, I was disappointed to find that although it coupled the lenses nicely to the K50 I couldn't focus either lens. I guess the lenses weren't able to project an image to the plane of the sensor in my camera. If that's the case, what good is this type of Leica-Pentax adapter. Am I missing something? What say ye learned Pentatians?

01-07-2020, 07:19 PM - 2 Likes   #2
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The problem lies in that that Leica Thread Mount has a flange distance of 28.8mm, and the K mount of 45.46mm. This means that an adapter that is flush with the mount would still have an increase of 16.66mm. This would be like using a 16.66mm extension tube, resulting in the inability for infinity focus. The only workarounds are to have an adapter with corrective glass (which lowers IQ), use the lenses on a mirrorless body with a short flange distance, or to take macro shots with them.
01-07-2020, 11:52 PM - 1 Like   #3
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^^^ This.

You could use the lens successfully on one of the mirrorless camera platforms with the correct adapter, since they have much shorter flange focal distances due to the absence of a mirror box. This is the reason mirrorless cameras are so popular with folks that like to tinker with adapted lenses. I use a Sony A7 MkII for my adapted lens work.

There's a useful wikipedia article that lists all of the flange focal distances for different systems:

Flange focal distance - Wikipedia
01-08-2020, 04:38 AM   #4
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Bertwert and BigmackCam, thanks for your comments. They explain everything. Come to think of it, I have a set of three extension tubes that I bought years ago and I'm pretty sure they have the Pentax screw thread. I'll dig them out and see what I can do with them. Thanks again.

01-08-2020, 08:45 AM   #5
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QuoteOriginally posted by psoo Quote
Bertwert and BigmackCam, thanks for your comments. They explain everything. Come to think of it, I have a set of three extension tubes that I bought years ago and I'm pretty sure they have the Pentax screw thread. I'll dig them out and see what I can do with them. Thanks again.
Using extension tubes will just increase your problem, you'll have an even longer distance between the sensor and lens (or flange distance). This means that you will have a focal point really close to the lens, so you could do some macro shots, or maybe even a focal point inside the lens, meaning that you won't be able to focus at all.

To use the lenses on digital, you would need to use another camera, one that is mirror less with a shorter flange distance (see Mike's linked article above). For example, a Sony A7, I'm not sure how much the original ones go for now. Other options include (with smaller sensors, mind that) the Micro-Four Thirds system and Pentax Q, as well as others.
01-08-2020, 10:31 AM   #6
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This thread also highlights why there are so many wonderful little gadgets you can buy on line, but can't find at a local camera store (if you still have one in your locale).

Technically, the poster received what was ordered. It does indeed fit a Leica mount lens to a K body. And since it cost very little, there's little point in sending it back. If you found one at your local store, you'd be back a few days later saying "hey, this adapter you sold me doesn't allow focus past a few millimeters. It's useless to me."

I notice there's a lot of stuff like that out there, that promises some utility that is really impossible to deliver - or has a really limited application. In this instance, putting a Leica thread enlarging lens onto a K bellows makes for a pretty nifty super macro outfit. But I would wager most get sold to those hoping to fit a vintage lens onto a modern body and focus all the way to infinity.

There's a reason the local camera store doesn't stock all this weird and wacky stuff you can readily find online. It would take only a few minutes in the store to realize it didn't deliver, and you wouldn't buy it. But a few clicks of a mouse and a couple of weeks shipping, and you're stuck with it.


And let's not get started on inexpensive flash units that look just like the expensive ones, and have all kinds of buttons that aren't hooked up to anything.
01-08-2020, 12:15 PM   #7
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QuoteOriginally posted by bertwert Quote
Using extension tubes will just increase your problem, you'll have an even longer distance between the sensor and lens (or flange distance). This means that you will have a focal point really close to the lens, so you could do some macro shots, or maybe even a focal point inside the lens, meaning that you won't be able to focus at all.

To use the lenses on digital, you would need to use another camera, one that is mirror less with a shorter flange distance (see Mike's linked article above). For example, a Sony A7, I'm not sure how much the original ones go for now. Other options include (with smaller sensors, mind that) the Micro-Four Thirds system and Pentax Q, as well as others.
Yes, of course, you're right. Better forget about the extension tubes.
01-08-2020, 04:12 PM   #8
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Just for reference, a few years ago I did a quick test with some of my M39 Russian rangefinder lenses, one of my Pentax DSLR's, an OEM M42-PK adaptor and an M39-M42 double-threaded ring, the sort you can buy to use the old Russian 39mm-screw slr lenses on an M42 mount. This arrangement allows the rangefinder lens to mount flush to the DSLR body, so is in effect as close as you can practically go.

My Jupiter 9 85mm f/2 focussed at about 2ft., the Jupiter 11 135mm f/4 focussed at about 4ft.. I've no notes regarding anything shorter, but if I remember correctly, the distance between the lens and the subject was impractically close with a 50mm lens and focus was totally unachievable with the two 28mm lenses I had.

Trust this might be of interest

01-08-2020, 06:57 PM   #9
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QuoteOriginally posted by kypfer Quote
Just for reference, a few years ago I did a quick test with some of my M39 Russian rangefinder lenses, one of my Pentax DSLR's, an OEM M42-PK adaptor and an M39-M42 double-threaded ring, the sort you can buy to use the old Russian 39mm-screw slr lenses on an M42 mount. This arrangement allows the rangefinder lens to mount flush to the DSLR body, so is in effect as close as you can practically go.

My Jupiter 9 85mm f/2 focussed at about 2ft., the Jupiter 11 135mm f/4 focussed at about 4ft.. I've no notes regarding anything shorter, but if I remember correctly, the distance between the lens and the subject was impractically close with a 50mm lens and focus was totally unachievable with the two 28mm lenses I had.

Trust this might be of interest
Thanks Kypfer. The ability to only focus at such short distances is very restrictive, isn't it? I don't think it's worth the effort when I have other lenses that will do the same job more efficiently. I was just curious about the legendary quality of these two Leica threaded lenses. I guess the best way to find out is to pop a 35 mm film into the cameras and find out the old way.
01-09-2020, 01:26 AM   #10
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QuoteOriginally posted by psoo Quote
Thanks Kypfer. The ability to only focus at such short distances is very restrictive, isn't it? I don't think it's worth the effort when I have other lenses that will do the same job more efficiently. I was just curious about the legendary quality of these two Leica threaded lenses. I guess the best way to find out is to pop a 35 mm film into the cameras and find out the old way.


Maybe you've got a friend or can find a contact locally who has a mirrorless camera you could borrow? If you're really lucky they'll have an M39 adaptor as well, else suitable adaptors are usually available quite cheaply, screw-thread being far easier to manufacture than a female bayonet
Already owning a selection of rangefinder lenses was my stimulus to acquire a Samsung NX5 when one became available locally at a very "sensible" price I get a lot of satisfaction from producing pin-sharp contrasty images with a rig that cost less than some pay for a polarising filter for their modern zoom lenses
02-13-2020, 09:34 AM   #11
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QuoteOriginally posted by kypfer Quote
Maybe you've got a friend or can find a contact locally who has a mirrorless camera you could borrow? If you're really lucky they'll have an M39 adaptor as well, else suitable adaptors are usually available quite cheaply, screw-thread being far easier to manufacture than a female bayonet
Already owning a selection of rangefinder lenses was my stimulus to acquire a Samsung NX5 when one became available locally at a very "sensible" price I get a lot of satisfaction from producing pin-sharp contrasty images with a rig that cost less than some pay for a polarising filter for their modern zoom lenses
HI Kypfer. I have been rethinking your comment about the use of a mirrorless camera with Leica type M39 threaded lenses. I already have an adapter that allows M39 lenses to be used on my K50. I was looking at the specifications for the mirrorless Pentax K-01 camera. Do you think that this body will be suitable for M39 lenses, as well as old Pentax lenses. If so, I'll probably buy one.
02-13-2020, 11:35 AM   #12
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QuoteOriginally posted by psoo Quote
HI Kypfer. I have been rethinking your comment about the use of a mirrorless camera with Leica type M39 threaded lenses. I already have an adapter that allows M39 lenses to be used on my K50. I was looking at the specifications for the mirrorless Pentax K-01 camera. Do you think that this body will be suitable for M39 lenses, as well as old Pentax lenses. If so, I'll probably buy one.
No, not at all!

The K-01 is effectively a K-mount Pentax DSLR without a mirror, so it has the same physical restrictions regarding the mounting of a lens, unless you want to get really adventurous and try poking the back of a collapsible Elmar or Industar into the body. I'll emphasise at this point I've not tried this, I don't know if there's sufficient clearance or if there's any possibility of doing any damage ... Not Recommended!!

Leica-type screw-fit lenses are designed to be used on a camera that is effectively 28.8mm "thick". Many (most?) modern mirrorless interchangeable-lens cameras are "thinner" than this, so a mechanical adaptor is not a problem. The Pentax K-mount however is effectively 45.46mm "thick" (as is M42-screw) so trying to fit any lens that was designed to be use on a "thinner" camera really is a non-starter!

Do note, none of this applies to the Russian SLR lenses designed for use with the Zenit 3m and similar cameras. These have a 39mm thread but are designed for use on a "thick" camera, coincidently of very similar "thickness" to a Pentax DSLR, so these can usually be adapted with no problem
02-13-2020, 07:47 PM   #13
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QuoteOriginally posted by kypfer Quote
No, not at all!

The K-01 is effectively a K-mount Pentax DSLR without a mirror, so it has the same physical restrictions regarding the mounting of a lens, unless you want to get really adventurous and try poking the back of a collapsible Elmar or Industar into the body. I'll emphasise at this point I've not tried this, I don't know if there's sufficient clearance or if there's any possibility of doing any damage ... Not Recommended!!

Leica-type screw-fit lenses are designed to be used on a camera that is effectively 28.8mm "thick". Many (most?) modern mirrorless interchangeable-lens cameras are "thinner" than this, so a mechanical adaptor is not a problem. The Pentax K-mount however is effectively 45.46mm "thick" (as is M42-screw) so trying to fit any lens that was designed to be use on a "thinner" camera really is a non-starter!

Do note, none of this applies to the Russian SLR lenses designed for use with the Zenit 3m and similar cameras. These have a 39mm thread but are designed for use on a "thick" camera, coincidently of very similar "thickness" to a Pentax DSLR, so these can usually be adapted with no problem
Thanks Kypfer, I now understand. Better put my Leica thread lenses in storage and stick to my Pentax ones.
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